Pneumatic tire

ABSTRACT

In a pneumatic tire, a groove depth H1 of each of first and second inclined lug grooves over an entire region from an opening portion to a corresponding one of first or second circumferential main grooves to a terminating end portion within a center land portion has a relationship with a maximum groove depth Hg of the corresponding one of the first or second circumferential main grooves represented by 0.80≤H1/Hg≤1.00. Additionally, a maximum groove depth H2 of each of first and second lateral grooves has a relationship with a groove depth H1e at a terminating end portion of the corresponding one of the first and second inclined lug grooves represented by 0.70≤H2/H1e≤0.90.

RELATED APPLICATION

This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2019-121682, filed Jun. 28, 2019, the entire contents of which is incorporated herein by reference.

TECHNICAL FIELD

The technology relates to a pneumatic tire and particularly relates to a pneumatic tire that can provide improved mud performance of the tire.

BACKGROUND ART

Known off-road tires include a plurality of inclined lug grooves formed on a tread surface and each having a groove depth equivalent to that of a main groove, in order to ensure appropriate traction characteristics while driving on a mud road. The technology described in Japan Unexamined Patent Publication No. 2015-227114 is a conventional pneumatic tire that is configured in this manner.

SUMMARY

The technology provides a pneumatic tire that can provide improved mud performance of the tire.

A pneumatic tire according to an embodiment of the technology corresponds to a pneumatic tire including: first and second circumferential main grooves extending in a tire circumferential direction; and a pair of shoulder land portions and one row of a center land portion defined by the first and second circumferential main grooves,

the center land portion comprising: a first inclined lug groove extending at an incline with respect to the tire circumferential direction and opening, at one end portion, to the first circumferential main groove and terminating, at another end portion, within the center land portion; a second inclined lug groove extending at an incline in a direction identical to a direction of the first inclined lug groove and opening, at one end portion, to the second circumferential main groove and terminating, at another end portion, within the center land portion; a first lateral groove connecting the first inclined lug groove with the second circumferential main groove; a second lateral groove connecting the second inclined lug groove with the first circumferential main groove; first and second auxiliary grooves connecting the first inclined lug groove with the second inclined lug groove adjacent to each other; and a plurality of center block defined by the grooves,

a groove depth H1 of the first inclined lug groove over an entire region from an opening portion to the first circumferential main groove to a terminating end portion within the center land portion having a relationship with a maximum groove depth Hg of the first circumferential main groove represented by 0.80≤H1/Hg≤1.00, and

a maximum groove depth H2 of the first lateral groove having a relationship with a groove depth H1e at the terminating end portion of the first inclined lug groove represented by 0.70≤H2/H1e≤0.90.

In the pneumatic tire according to the technology, (1) the inclined lug groove terminates within the center land portion without extending through the center land portion. Thus, compared to a configuration in which the inclined lug groove extends through the center land portion, this configuration provides an increased mud column shear force during traveling on a mud road. This has the advantage of improving the traction characteristics of the tire, improving the mud performance the tire. Additionally, (2) the maximum groove depth H2 of the lateral groove is shallower than the groove depth H1e of the terminating end portion of the inclined lug groove, thus producing an effect that holds back a flow path (that is, the lateral groove) from the inclined lug groove to the circumferential main groove. Thus, advantageously, the terminating end portion of the inclined lug groove has an increased soil column shear force, further improving the mud performance of the tire.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a cross-sectional view in a tire meridian direction illustrating a pneumatic tire according to an embodiment of the technology.

FIG. 2 is a plan view illustrating a tread surface of the pneumatic tire illustrated in FIG. 1 .

FIG. 3 is an enlarged view illustrating a center land portion illustrated in FIG. 2 .

FIG. 4 is a cross-sectional view of the center land portion taken along line X-X in FIG. 3 .

FIG. 5 is an explanatory diagram illustrating first center blocks of the center land portion illustrated in FIG. 3 .

FIG. 6 is an explanatory diagram illustrating second center blocks of the center land portion illustrated in FIG. 3 .

FIG. 7 is an enlarged view illustrating a notch portion illustrated in FIG. 5 .

FIGS. 8A-8C include a table showing the results of performance tests of pneumatic tires according to embodiments of the technology.

DETAILED DESCRIPTION

Embodiments of the technology are described in detail below with reference to the drawings. However, the technology is not limited to these embodiments. Moreover, constituents of the embodiments include elements that are substitutable while maintaining consistency with the technology, and obviously substitutable elements. Furthermore, the modified examples described in the embodiments can be combined as desired within the scope apparent to one skilled in the art.

Pneumatic Tire

FIG. 1 is a cross-sectional view in a tire meridian direction illustrating a pneumatic tire according to an embodiment of the technology. The same drawing illustrates a cross-sectional view of a half region in a tire radial direction. Additionally, the same drawing illustrates a radial tire for a light truck as an example of a pneumatic tire.

In reference to the same drawing, a cross-section in a tire meridian direction is defined as a cross-section of the tire taken along a plane that includes a tire rotation axis (not illustrated). Additionally, a tire equatorial plane CL is defined as a plane extending perpendicularly to the tire rotation axis through the midpoint of measurement points of a tire cross-sectional width defined by JATMA. Additionally, a tire lateral direction is defined as the direction parallel with the tire rotation axis. The tire radial direction is defined as the direction perpendicular to the tire rotation axis.

A pneumatic tire 1 has an annular structure with the tire rotation axis as its center and includes a pair of bead cores 11, 11, a pair of bead fillers 12, 12, a carcass layer 13, a belt layer 14, a tread rubber 15, a pair of sidewall rubbers 16, 16, and a pair of rim cushion rubbers 17, 17 (see FIG. 1 ).

The pair of bead cores 11, 11 are formed by winding one or a plurality of bead wires made of steel in an annular shape and in multiple layers and are embedded in respective bead portions to form cores of the left and right bead portions. The pair of bead fillers 12, 12 are disposed outward of the pair of bead cores 11, 11 in the tire radial direction and reinforce the bead portions.

The carcass layer 13 has a single layer structure made of one carcass ply or a multilayer structure made of a plurality of carcass plies and extends between the left and right bead cores 11, 11 in a toroidal shape, forming the framework of the tire. Additionally, both end portions of the carcass layer 13 are turned back outward in the tire lateral direction so as to wrap around the bead cores 11 and the bead fillers 12 and fixed. Additionally, carcass plies in the carcass layer 13 are made by performing a rolling process on coating rubber-covered carcass cords made of steel or an organic fiber material (e.g. aramid, nylon, polyester, rayon, or the like). Each of the carcass plies has a cord angle (defined as the inclination angle, in the longitudinal direction, of the carcass cords with respect to the tire circumferential direction) of 80 deg. or more and 100 deg. or less.

The belt layer 14 is a multilayer structure including a plurality of belt plies 141 to 143 and is disposed by being wound around the outer circumference of the carcass layer 13. The belt plies 141 to 143 include a pair of cross belts 141, 142 and a belt cover 143.

The pair of cross belts 141, 142 are made by performing a rolling process on coating rubber-covered belt cords made of steel or an organic fiber material. Each of the cross belts 141, 142 has a cord angle of 15 deg. or more and 55 deg. or less as absolute values. Additionally, the pair of cross belts 141, 142 have cord angles (defined as inclination angles, in the longitudinal direction, of the belt cords with respect to the tire circumferential direction) of opposite signs and are layered such that the longitudinal directions the belt cords intersect each other (what is called a crossply structure). Additionally, the pair of cross belts 141, 142 are disposed layered outward of the carcass layer 13 in the tire radial direction.

The belt cover 143 is made by coating belt cover cords made of steel or an organic fiber material with coating rubber. The belt cover 143 has a cord angle of 0 deg. or more and 10 deg. or less as absolute values. Additionally, the belt cover 143 is, for example, a strip material formed by coating one or a plurality of belt cover cords with coating rubber and winding the strip material spirally around the outer circumferential surface of the cross belts 141, 142 a plurality of times in the tire circumferential direction. Additionally, the belt cover 143 is disposed covering the entire areas of the cross belts 141, 142.

The tread rubber 15 is disposed outward of the carcass layer 13 and the belt layer 14 in the tire radial direction and constitutes a tread portion. The pair of sidewall rubbers 16, 16 are disposed outward of the carcass layer 13 in the tire lateral direction and constitute left and right sidewall portions. Each of the pair of rim cushion rubbers 17, 17 extends, from an inner side of a corresponding one of the left and right bead cores 11, 11 and a turned back portion of the carcass layer 13 in the tire radial direction, outward in the tire width direction, forming a rim engaging surface of the bead portion.

Tread Pattern

FIG. 2 is a plan view illustrating a tread surface of the pneumatic tire illustrated in FIG. 1 . The same drawing illustrates a tread surface of an off-road tire. In reference to the same drawing, “tire circumferential direction” refers to the direction revolving about the tire rotation axis. A reference sign T denotes a tire ground contact edge, and a dimensional sign TW denotes a tire ground contact width.

As illustrated in FIG. 2 , the pneumatic tire 1 includes, in a tread surface, a pair of circumferential main grooves 2A, 2B; and a pair of shoulder land portions 31A, 31B and one row of a center land portion 32 defined by the circumferential main grooves 2A, 2B.

Each of the circumferential main grooves 2A, 2B has a zigzag shape with an amplitude in the tire lateral direction. Additionally, each of the circumferential main grooves 2A, 2B is obliged to include a wear indicator specified by JATMA (The Japan Automobile Tyre Manufacturers Association, Inc.) and typically has a groove width of 7.0 mm or more and a groove depth of 8.5 mm or more.

The groove width is measured as a distance between opposing groove walls at a groove opening portion with the tire mounted on a specified rim and inflated to a specified internal pressure and in an unloaded state. In a configuration including a notch portion or a chamfered portion at the groove opening portion, the groove width is measured using, as measurement points, intersection points between an extension line of a tread contact surface and extension line of the groove walls, in a cross-sectional view parallel to a groove width direction and a groove depth direction.

The groove depth is measured as a distance from the tread contact surface to a maximum groove depth position with the tire mounted on a specified rim and inflated to the specified internal pressure and in an unloaded state. Additionally, in a configuration in which a partial recess/protrusion portion and a sipe at the groove bottom, the groove depth is measured by excluding these portions.

“Specified rim” refers to a “standard rim” defined by JATMA, a “Design Rim” defined by TRA (The Tire and Rim Association, Inc.), or a “Measuring Rim” defined by ETRTO (The European Tyre and Rim Technical Organisation). Additionally, “specified internal pressure” refers to a “maximum air pressure” defined by JATMA, the maximum value in “TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES” defined by TRA, or “INFLATION PRESSURES” defined by ETRTO. Additionally, “specified load” refers to a “maximum load capacity” defined by JATMA, the maximum value in “TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES” defined by TRA, or “LOAD CAPACITY” defined by ETRTO. However, in JATMA, for a passenger vehicle tire, the specified internal pressure is an air pressure of 180 kPa, and the specified load is 88% of the maximum load capacity at the specified internal pressure.

Additionally, in the configuration in FIG. 2 , the pneumatic tire 1 has a substantially point-symmetric tread pattern with a center point on the tire equatorial plane CL. However, no such limitation is intended, and the pneumatic tire 1 may have a point-asymmetric tread pattern (not illustrated).

Additionally, in FIG. 2 , a maximum ground contact width Wb1 of each of the shoulder land portion 31A, 31B with respect to the tire ground contact width TW is preferably in the range of 0.50≤Wb1/TW≤0.80 and more preferably in the range of 0.55≤Wb1/TW≤0.70.

Additionally, a maximum ground contact width Wb2 of the center land portion 32 with respect to the tire ground contact width TW is preferably in the range of 0.30≤Wb2/TW≤0.60 and more preferably in the range of 0.40≤Wb2/TW≤0.50.

The ground contact width of a land portion is measured as a linear distance in the tire axial direction on a contact surface between the land portion and a flat plate, with the tire mounted on a specified rim, inflated to the specified internal pressure, and placed perpendicularly to the flat plate in a stationary state and loaded with a load corresponding to the specified load.

The tire ground contact width TW is measured as a linear distance in the tire axial direction on a contact surface between the tire and a flat plate, with the tire mounted on a specified rim, inflated to the specified internal pressure, and placed perpendicularly to the flat plate in a stationary state and loaded with a load corresponding to the specified load.

The tire ground contact edge T is defined as the maximum width position in the tire axial direction of the contact surface between the tire and a flat plate, with the tire mounted on a specified rim, inflated to the specified internal pressure, and placed perpendicularly to the flat plate in a stationary state and added with a load corresponding to the specified load.

Additionally, as illustrated in FIG. 2 , the pair of shoulder land portions 31A, 31B and the center land portion 32 are disposed overlapping each other as viewed in the tire circumferential direction. Accordingly, the circumferential main grooves 2A, 2B have a see-through-less structure as viewed in the tire circumferential direction.

Additionally, an overlapping amount Db between each of the shoulder land portions 31A, 31B and the center land portion 32 has a relationship with the tire ground contact width TW represented by 0≤Db/TW≤0.10.

The overlapping amount Db of each of the land portions 31A, 31B, 32 is measured as a distance in the tire lateral direction between the measurement points of the maximum ground contact widths Wb1, Wb2 of the land portion 31A, 31B, 32.

Shoulder Land Portions

As illustrated in FIG. 2 , each of the shoulder land portions 31A, 31B includes a plurality of shoulder lug grooves 311 and a plurality of shoulder blocks 312 defined by the shoulder lug grooves 311.

Each of the shoulder lug grooves 311 extends in the tire lateral direction, opens, at one end portion, to the circumferential main groove 2A, 2B, and opens, at the other end portion, to the tire ground contact edge T. Additionally, the plurality of the shoulder lug grooves 311 are arranged at predetermined intervals in the tire circumferential direction. In addition, each of the shoulder lug grooves 311 has a groove width of 13 mm or more and a groove depth of 8.0 mm or more. The groove depth of the shoulder lug groove 311 with respect to the groove depth of the circumferential main groove 2A is in the range of 80% or more and 100% or less. Additionally, in the configuration in FIG. 2 , the shoulder lug grooves 311 are disposed, the number of which is the same as the pitch number of the zigzag shape of the circumferential main grooves 2A, and each of the shoulder lug grooves 311 opens at a maximum amplitude position of the circumferential main groove 2A, 2B outward in the tire lateral direction.

The shoulder block 312 has a convex edge portion protruding toward the tire equatorial plane CL along the zigzag shape of the circumferential main groove 2A, 2B. Additionally, the plurality of shoulder blocks 312 are arranged at predetermined intervals in the tire circumferential direction to form a single block row. Additionally, in the configuration of FIG. 2 , the shoulder blocks 312 are formed, the number of which is the same as the pitch number of the zigzag shape of the circumferential main grooves 2A. Additionally, each of the shoulder blocks 312 includes: a semi-closed lug groove (reference sign omitted in drawings) that opens, at one end portion, to the tire ground contact edge T and that terminates, at the other end portion, within the shoulder block 312, a plurality of sipes (reference sign omitted in drawings); and pin holes (reference sign is omitted in the drawings) into which studless pins are inserted.

Center Land Portion

FIG. 3 is an enlarged view illustrating the center land portion illustrated in FIG. 2 . FIG. 4 is a cross-sectional view of the center land portion taken along line X-X in FIG. 3 .

As illustrated in FIG. 3 , the center land portion 32 includes: first and second inclined lug grooves 321A, 321B; first and second lateral grooves 322A, 322B; first and second auxiliary grooves 323A, 323B; and a plurality of center blocks 41A, 41B, 42A, 42B defined by the grooves.

As illustrated in FIG. 2 , each of the first inclined lug grooves 321A extends at an incline with respect to the tire circumferential direction and intersects the tire equatorial plane CL. Additionally, the first inclined lug groove 321A opens, at one end portion, to the first circumferential main groove 2A and terminates, at the other end portion, within the center land portion 32. The each of second inclined lug grooves 321B extends at an incline in the same direction as the first inclined lug grooves 321A and intersects the tire equatorial plane CL. Additionally, each of the second inclined lug grooves 321B opens, at one end portion, to the second circumferential main groove 2B and terminates, at the other end portion, within the center land portion 32. Accordingly, the first and second inclined lug grooves 321A, 321B are inclined in the same direction with respect to the tire circumferential direction and open to the different circumferential main grooves 2A, 2B.

Additionally, each of the first and second inclined lug grooves 321A, 321B has a groove width of 5.0 mm or more and a groove depth of 8.0 mm or more. In the configuration in FIG. 3 , the first and second inclined lug grooves 321A, 321B are main grooves and, as illustrated in FIG. 4 , have substantially the same maximum groove depth as that of the circumferential main grooves 2A, 2B. Specifically, a groove depth H1 of the inclined lug groove 321A, 321B over the entire area from the opening portion at the circumferential main groove 2A, 2B to the terminating end portion in the center land portion 32 has a relationship with a maximum groove depth Hg of the circumferential main groove 2A, 2B represented by 0.80≤H1/Hg≤1.00 and more preferably by 0.90≤H1/Hg≤1.00. Thus, each of the inclined lug grooves 321A, 321B is defined as a continuous groove portion having the groove depth H1 described above, and the terminating end portion is defined as the end portion of the above-described groove portion in the center land portion 32.

In the configuration described above, each of the inclined lug grooves 321A, 321B terminates within the center land portion 32 without extending through the center land portion 32. Thus, compared to a configuration in which the inclined lug groove extends through the center land portion (not illustrated), this configuration provides an increased soil column shear force during traveling on a mud road. Thus, the traction characteristics of the tire are improved and the mud performance of the tire is improved. Additionally, the rigidity of the center blocks 41A to 42B is increased to improve the wear resistance performance of the tire.

Additionally, in FIG. 3 , an inclination angle θ1 of each of the first and second inclined lug grooves 321A, 321B in the tire equatorial plane CL is preferably in the range of 25 deg.≤θ1≤70 deg. and more preferably in the range of 30 deg.≤θ1≤50 deg.

The inclination angle θ1 of the inclined lug groove is measured as an angle between the groove center line of the inclined lug groove and the tire equatorial plane CL.

For example, in the configuration in FIG. 3 , the first and second inclined lug grooves 321A, 321B are main grooves and each have a groove depth equivalent to that of each of the circumferential main grooves 2A, 2B. In addition, both the first and second inclined lug grooves 321A, 321B extend from the first and second circumferential main grooves 2A, 2B to a position where the inclined lug grooves intersect the tire equatorial plane CL. Additionally, the inclined lug groove 321A, 321B includes a widened portion (reference sign is omitted in drawings) between the terminating end portion of the inclined lug groove and the tire equatorial plane CL.

Additionally, in FIG. 3 , a distance D1 from the tire equatorial plane CL to the terminating end portion of each of the first and second inclined lug grooves 321A, 321B has a relationship with the tire ground contact width TW represented by 0≤D1/TW≤0.20. Thus, the terminating end portions of the inclined lug grooves 321A, 321B are appropriately positioned, improving the tire traction characteristics of the tire.

In the configuration illustrated in FIG. 3 , both the first and second inclined lug grooves 321A, 321B extend in the tire lateral direction beyond the tire equatorial plane CL, and thus overlap each other. However, no such limitation is intended, and one or both of the inclined lug grooves 321A, 321B may terminate without intersecting the tire equatorial plane CL (not illustrated). The inclined lug grooves 321A, 321B may terminate without overlapping each other as viewed in the tire circumferential direction or in the tire lateral direction (not illustrated).

The first lateral groove 322A connects the first inclined lug groove 321A with the second circumferential main groove 2B. The second lateral groove 322B connects the second inclined lug groove 321B with the first circumferential main groove 2A. Additionally, the single lateral groove 322A, 322B opens with respect to the set of the inclined lug groove 321A, 321B and the circumferential main groove 2B, 2A.

Additionally, each of the first and second lateral grooves 322A, 322B has a groove width of 4.0 mm or more and 20 mm or less and a groove depth of 6.0 mm or more and 17 mm or less. In the configuration of FIG. 3 , as illustrated in FIG. 4 , each of the first and second lateral grooves 322A, 322B has a smaller groove width and a smaller groove depth than each of the circumferential main grooves 2A, 2B and each of the inclined lug grooves 321A, 321B. Additionally, a maximum groove depth H2 of the lateral groove 322A, 322B preferably has a relationship with a groove depth H1e at the terminating end portion of the inclined lug groove 321A, 321B represented by 0.70≤H2/H1e≤0.90 and more preferably by 0.75≤H2/H1e≤0.85.

In the configuration described above, the maximum groove depth H2 of the lateral groove 322A, 322B is shallower than the groove depth H1e of the terminating end portion of the inclined lug groove 321A, 321B, thus ensuring an effect that holds back a flow path (that is, the lateral groove 322A, 322B) from the inclined lug groove 321A, 321B to the circumferential main groove 2B, 2A. Accordingly, the terminating end portion of the inclined lug groove 321A, 321B has an increased soil column shear force, further improving the mud performance of the tire. Additionally, a raised bottom effect of the lateral groove 322A, 322B increases the rigidity of the center blocks 41A to 42B, improving the wear resistance performance of the tire.

Additionally, an inclination angle θ2 of each of the first and second lateral grooves 322A, 322B with respect to the tire circumferential direction is preferably in the range of 80 deg.≤θ2≤120 deg. and more preferably in the range of 85 deg.≤θ2≤100 deg. Thus, the first and second lateral grooves 322A, 322B are substantially orthogonal to the tire circumferential direction. The inclination angles θ2 of the lateral grooves 322A, 322B are measured as angles formed between the tire circumferential direction and a straight line extending through the left and right opening portions of the inclined lug grooves 321A, 321B opening to the circumferential main grooves 2A, 2B.

Additionally, in FIG. 3 , a crossing angle α of each of the first and second lateral grooves 322A, 322B with respect to the corresponding one of the second and first inclined lug grooves 321A, 321B is preferably in the range of 30 deg.≤α≤75 deg. and more preferably in the range of 40 deg.≤α≤60 deg.

The crossing angle α is measured as an angle formed between an extension line of the groove center line of the lateral groove 322A, 322B and the groove center line of the inclined lug groove 321A, 321B.

In the configuration described above, the lateral groove 322A, 322B connecting the circumferential main groove 2A, 2B with the inclined lug groove 321A, 321B opens laterally at an angle of 30 deg. or more relative to the inclined lug groove 321A, 321B. Thus, a groove unit from the inclined lug groove 321A, 321B to the circumferential main groove 2A, 2B via the lateral groove 322A, 322B has an L- or T-bent shape. Thus, the terminating end portion of the inclined lug groove 321A, 321B has an increased soil column shear force, improving the traction characteristics of the tire.

In FIG. 3 , a distance D12 to the tire equatorial plane CL from the intersection point between the groove center line of each of the second and first inclined lug grooves 321A, 321B and the groove center line of the corresponding one of the first and second lateral grooves 322A, 322B preferably has a relationship with the tire ground contact width TW (see FIG. 2 ) represented by 0≤D12/TW≤0.20. For example, in the configuration of FIG. 3 , the lateral grooves 322A, 322B are connected to the inclined lug grooves 321A, 321B in the region between the terminating end portions of the inclined lug grooves 321A, 321B and the tire equatorial plane CL.

The opening position of the lateral grooves 322A, 322B is defined as the midpoint of the measurement points of the opening width of the first and second lateral grooves 322A, 322B with respect to the inclined lug grooves 321A, 321B.

In FIG. 3 , an extension length D2 of each of the first and second lateral grooves 322A, 322B in the tire lateral direction has a relationship with a maximum ground contact width Wb2 of the center land portion 32 represented by 0.10≤D2/Wb2≤0.30.

Additionally, in FIG. 3 , a distance L2, in the tire circumferential direction, of the opening position of each of the first and second lateral grooves 322A, 322B with respect to the corresponding one of the second and first inclined lug grooves 321A, 321B preferably has a relationship with a pitch length P2 of the center block 41A represented by 0≤L2/P2≤0.30.

Each of the first and second auxiliary grooves 323A, 323B connects the first inclined lug grooves 321A with the second inclined lug grooves 321B, which are adjacent to each other. Additionally, the first and second auxiliary grooves 323A, 323B are disposed alternately in the tire circumferential direction.

Additionally, each of the first and second auxiliary grooves 323A, 323B has a groove width of 2.0 mm or more and 23 mm or less and a groove depth of 6.0 mm or more and 17 mm or less. In the configuration of FIG. 3 , each of the first and second auxiliary grooves 323A, 323B has a smaller groove depth than each of the circumferential main grooves 2A, 2B and each of the inclined lug grooves 321A, 321B. Specifically, a maximum groove depth H3 (not illustrated) of each of the first and second auxiliary grooves 323A, 323B preferably has a relationship with the groove depth H1 (see FIG. 4 ) of each of the first and second inclined lug grooves 321A, 321B represented by 0.70≤H3/H1≤0.90 and more preferably by 0.75≤H3/H1≤0.85.

In addition, inclination angles θ3A, 03B of the first and second auxiliary grooves 323A, 323B are preferably in the range of 10 deg.≤θ3A≤30 deg. and 30 deg.≤θ3B≤85 deg. and more preferably in the range of 15 deg.≤θ3A≤25 deg. and 40 deg.≤θ3B≤80 deg. Additionally, the inclination angle θ3A of the first auxiliary groove 323A with respect to the tire circumferential direction is smaller than the inclination angle θ3B of the second auxiliary groove 323B. Specifically, a difference between the inclination angles θ3A and 03B is preferably in the range of 15 deg.≤θ3A-θ3B.

The inclination angles θ3A, 03B of the auxiliary grooves 323A, 323B are measured as angles formed between the tire circumferential direction and a straight line extending through the left and right opening portions of the inclined lug grooves 321A, 321B.

For example, in the configuration in FIG. 3 , the first and second auxiliary grooves 323A, 323B are disposed on the tire equatorial plane CL and define the center blocks 41A to 42B. Additionally, each of the first auxiliary grooves 323A defines the first center blocks 41A, 41B, described below, and each of the second auxiliary grooves 323B defines the second center blocks 42A, 42B, described below. Additionally, the first and second auxiliary grooves 323A, 323B have different inclination angles θ3A, θ3B and are inclined in the same direction with respect to the tire circumferential direction.

Center Block

FIGS. 5 and 6 are explanatory diagrams illustrating center blocks of the center land portion illustrated in FIG. 3 . In these drawings, FIG. 5 illustrates a pair of first center blocks 41A, 41B, and FIG. 6 illustrates a pair of center blocks 42A, 42B.

As illustrated in FIG. 2 , the center blocks 41A, 41B, 42A, 42B are defined into the grooves described above, that is, the first and second circumferential main grooves 2A, the first and second inclined lug grooves 321A, 321B, the first and second lateral grooves 322A, 322B, and the first and second auxiliary grooves 323A, 323B.

Here, of the plurality of center blocks 41A, 41B, 42A, 42B, the center blocks 41A, 41B disposed on an extension line of the groove center lines of the first and second inclined lug grooves 321A, 321B are defined as first center blocks. Additionally, the center blocks 42A, 42B disposed between the first and second inclined lug grooves 321A, 321B are defined as second center blocks. In the configuration of FIG. 2 , the pair of center blocks 41A, 41B are defined as first center blocks, and the pair of center blocks 42A, 42B are defined as second center blocks.

In the configuration in FIG. 2 , block units (reference sign omitted in drawings) each including a set of the pair of first center blocks 41A, 41B and the pair of second center blocks 42A, 42B are arranged repeatedly in the tire circumferential direction to form a block row of the center land portion 32. Additionally, as illustrated in FIG. 3 , the first center block 41A and the second center block 42B, located on the left side of FIG. 3 , are disposed in a row in the tire circumferential direction with edge portions on the first circumferential main groove 2A side aligned with each other. In addition, the first center block 41B and the second center block 42A, located on the right side of FIG. 3 , are disposed in a row in the tire circumferential direction along the second circumferential main groove 2B with edge portions on the tire lateral direction outer side aligned with each other. Additionally, the left and right first center blocks 41A, 41B are disposed offset from each other in the tire circumferential direction, and the left and right second center blocks 42A, 42B are disposed offset from each other in the tire circumferential direction.

Note that, in the configuration in FIG. 2 , one block unit includes the pair of first center blocks 41A, 41B and the pair of second center blocks 42A, 42B as described above. However, no such limitation is intended, and one block unit may include a pair of first center blocks and two or more (for example, three) second center blocks (not illustrated). Even in this case, the first center blocks and the second center blocks are alternately arranged in the tire circumferential direction to form a block row of the center land portion 32.

Additionally, in the configuration in FIG. 3 , each of the first and second lateral grooves 322A, 322B has the inclination angle θ2 substantially orthogonal to the tire circumferential direction as described above. Thus, the center blocks 41A to 42B defined by the lateral grooves 322A, 322B include respective edge portions substantially orthogonal to the tire circumferential direction. This ensures edge components of the center blocks 41A to 42B, improving the mud performance of the tire.

Additionally, in FIGS. 5 and 6 , a maximum length Lb1 of the center blocks 41A to 42B in the tire circumferential direction and a maximum width Lb2 of the center blocks 41A to 42B in the tire lateral direction have a relationship of 0.70≤Lb2/Lb1≤1.10. In addition, the maximum length Lb1 of the center blocks 41A to 42B preferably has a relationship with the pitch length P2 (see FIG. 3 ) of the center block 41A represented by 0.40≤Lb1/P2≤0.70. Additionally, the maximum width Lb2 of the center blocks 41A to 42B preferably has a relationship with the tire ground contact width TW (see FIG. 2 ) represented by 0.10≤Lb2/TW≤0.50 and more preferably by 0.20≤Lb2/TW≤0.40.

The maximum length Lb1 and the maximum width Lb2 of the center blocks 41A to 42B are measured on the contact surface between the land portion and a flat plate, with the tire mounted on a specified rim, inflated to the specified internal pressure, and placed perpendicularly to the flat plate in a stationary state and loaded with a load corresponding to the specified load.

Notch Portion of Center Block

FIG. 7 is an enlarged view illustrating a notch portion illustrated in FIG. 5 .

In FIG. 3 , the first center blocks 41A, 41B are disposed on the extension line of the first and second inclined lug grooves 321A, 321B. Edge portions of the first center blocks 41A, 41B each include a first notch portion 51.

The first notch portion 51 is a groove-shaped recess portion opening in the block road contact surface. The first notch portion 51 is formed in an edge portion of the first center block 41A, 41B and opens to a terminating end portion of the first or second inclined lug groove 321A, 321B.

For example, in the configuration of FIG. 3 , the pair of first center blocks 41A, 41B each include the first notch portion 51, which is U shaped, and the first notch portions 51 are disposed on the extension line of the groove center lines of the first and second inclined lug grooves 321A, 321B to extend the terminating end portions of the inclined lug grooves 321A, 321B. Additionally, the first notch portion 51 opens at connecting portions between the inclined lug grooves 321A, 321B and the lateral grooves 322A, 322B.

In the configuration described above, the edge portions of the first center blocks 41A, 41B each include the first notch portion 51 opening at the corresponding one of the terminating end portions of the inclined lug grooves 321A, 321B, thus increasing the soil column shear force to improve a mud discharge function. Thus, the mud performance of the tire is improved.

Additionally, an opening area Sc of the first notch portion 51 with respect to an area Sb of the road contact surface of each of the first center blocks 41A, 41B is preferably in the range of 0.003≤Sc/Sb≤0.030 and more preferably in the range of 0.004≤Sc/Sb≤0.020.

As illustrated in FIG. 7 , the opening area Sc of the first notch portion 51 is calculated as the area of a closed region bounded by a normal line extended from an opening end of the first notch portion 51 on the lateral groove 322A (322B) side, toward the other wall surface, in a plan view of the first center block 41A (41B).

The area Sb of the road contact surface of the block is calculated as the area of a region of the block enclosed by a contour line in a tread plan view.

In FIG. 4 , a maximum depth Hc1 of the first notch portion 51 preferably has a relationship with the groove depth H1e of the terminating end portion of each of the inclined lug grooves 321A, 321B represented by 0.80≤Hc1/H1e≤1.00.

Additionally, in FIG. 3 , the second center blocks 42A, 42B are disposed between the first and second inclined lug grooves 321A, 321B as described above. Edge portions of the second center blocks 42A, 42B each include a second notch portion 52.

The second notch portion 52 is a groove-shaped recess portion that opens in the block road contact surface. The second notch portion 52 is formed at an edge portion of the second center block 42A, 42B and opens to the first or second circumferential main groove 2A, 2B.

For example, in the configuration of FIG. 3 , the pair of second center blocks 42A, 42B each include the second notch portion 52, which is V shaped, and the second notch portions 52 respectively open at maximum amplitude positions of the first and second circumferential main grooves 2A, 2B. Additionally, the second notch portion 52 opens at the connecting portion between the circumferential main grooves 2A, 2B and the lateral grooves 322A, 322B. Thus, the mud performance of the tire is improved.

Additionally, a maximum depth Hc2 (not illustrated) of the second notch portion 52 preferably has a relationship with the groove depth Hg (see FIG. 4 ) of each of the circumferential main grooves 2A, 2B (see FIG. 4 ) represented by 0.80≤Hc2/Hg≤1.00.

Additionally, as illustrated in FIGS. 5 and 6 , each of the center blocks 41A to 42B includes a through sipe 53, a pair of narrow grooves 54A, 54B, and a plurality of closed sipes 55.

The through sipes 53 extend through the center blocks 41A to 42B and open at left and right edge portions of the center blocks 41A to 42B.

The narrow grooves 54A, 54B extend along the through sipes 53. Each narrow groove 54A, 54B opens, at one end portion, to an edge portion of a corresponding one of the center blocks 41A to 42B and terminates, at the other end portion, within the corresponding one of the center blocks 41A to 42B. Additionally, a maximum groove depth Hs (not illustrated) of each narrow groove 54A, 54B has a relationship with the groove depth Hg of each circumferential main groove 2A, 2B (see FIG. 4 ) represented by 0.60≤Hs/Hg≤0.90.

Note that instead of the narrow grooves 54A, 54B, chamfered portions or what is called chamfered sipes may be formed that extend along the through sipes 53 and that open to the road contact surfaces of the center blocks 41A to 42B (not illustrated).

The closed sipes 55 terminate within the center blocks 41A to 42B. Additionally, a plurality of the closed sipes 55 are each disposed in one of the left and right regions of the center blocks 41A to 42B defined by the through sipes 53.

The sipes are cuts formed in the tread contact surface and each have a sipe width of less than 1.5 mm and a sipe depth of 2.0 mm or more. Thus, the sipes close when the tire comes into contact with the ground.

The sipe width is measured as the maximum opening width of the sipe on the tread contact surface, with the tire mounted on a specified rim and inflated to the specified internal pressure and in an unloaded state.

The sipe depth is measured as a distance from the tread contact surface to the maximum depth position of the sipe, with the tire is mounted on a specified rim and inflated to the specified internal pressure and in an unloaded state. Additionally, in a configuration in which a sipe partially includes a recess/protrusion portion on the groove bottom, the sipe depth is measured excluding this portion.

Note that in the configuration in FIG. 6 , each of the second center blocks 42A, 42B includes a chamfered portion 56 at an acute corner.

Effects

As described above, the pneumatic tire 1 includes the first and second circumferential main grooves 2A, 2B extending in the tire circumferential direction, and the pair of shoulder land portions 31A, 31B and the one row of the center land portion 32 defined by the first and second circumferential main grooves 2A, 2B (see FIG. 2 ). Additionally, the center land portion includes: the plurality of first inclined lug grooves 321A each extending at an incline with respect to the tire circumferential direction and opening, at one end portion, to the first circumferential main groove 2A and terminating, at the other end portion, within the center land portion 32; the plurality of second inclined lug grooves 321B each extending at an incline in the same direction as the first inclined lug grooves 321A and opening, at one end portion, to the second circumferential main groove 2B and terminating, at the other end portion, within the center land portion 32; the plurality of first lateral grooves 322A each connecting the first inclined lug groove 321A with the second circumferential main groove 2B; the plurality of second lateral grooves 322B each connecting the second inclined lug groove 321B and the first circumferential main groove 2A; the plurality of auxiliary grooves 323A, 323B each connecting the first inclined lug groove 321A with the second inclined lug groove 321B adjacent to each other; and the plurality of center blocks 41A, 41B, 42A, 42B defined by the grooves (see FIG. 3 ). Additionally, the maximum groove depth H1 of the first (and second) inclined lug groove 321A (321B) over the entire area from the opening to the first (and second) circumferential main groove 2A (2B) to the terminating end portion within the center land portion 32 has a relationship with the maximum groove depth Hg of the first (and second) circumferential main groove 2A (2B) represented by 0.80≤H1/Hg≤1.00 (see FIG. 4 ). Additionally, the maximum groove depth H2 of the first (and second) lateral groove 322A (322B) has a relationship with the groove depth H1e at the terminating end portion of the first (and second) inclined lug groove 321A (321B) represented by 0.70≤H2/H1≤0.90.

In the configuration as described above, (1) each of the inclined lug grooves 321A, 321B terminates within the center land portion 32 without extending through the center land portion 32. Thus, compared to a configuration in which the inclined lug groove extends through the center land portion (not illustrated), a soil column shear force during traveling on a snowy road is increased. This has the advantage of improving the traction characteristics of the tire, improving the mud performance the tire. Additionally, advantageously, the rigidity of the center blocks 41A to 42B is increased to improve the wear resistance performance of the tire.

Additionally, (2) the maximum groove depth H2 of the lateral groove 322A, 322B is shallower than the groove depth H1e of the terminating end portion of the inclined lug groove 321A, 321B, thus ensuring an effect that holds back a flow path (that is, the lateral groove 322A, 322B) from the inclined lug groove 321A, 321B to the circumferential main groove 2A, 2B. Thus, advantageously, the terminating end portion of the inclined lug groove 321A, 321B has an increased soil column shear force, further improving the mud performance of the tire. Additionally, advantageously, a raised bottom effect of the lateral groove 322A, 322B increases the rigidity of the center blocks 41A to 42B, improving the wear resistance performance of the tire.

Additionally, in the pneumatic tire 1, the plurality of center blocks 41A to 42B include the pair of first center blocks 41A, 41B disposed adjacent in the tire lateral direction and the two or more second center blocks 42A, 42B disposed adjacent in the tire lateral direction, the first center blocks 41A, 41B and the second center blocks 42A, 42B being alternately arranged in the tire circumferential direction (see FIG. 3 ). Additionally, the pair of first center blocks 41A, 41B are disposed on the extension line of the first and second inclined lug grooves 321A, 321B. Thus, advantageously, the center blocks 41A to 42B are appropriately disposed with respect to the inclined lug grooves 321A, 321B, improving the mud performance of the tire.

Additionally, in the pneumatic tire 1, the maximum width Lb2 (see FIGS. 5 and 6 ) of the center blocks 41A to 42B has a relationship with the tire ground contact width TW represented by 0.10≤Lb2/TW≤0.50. Advantageously, the above-described lower limit appropriately ensures the maximum width Lb2 of the center blocks 41A to 42B, suppressing uneven wear of the blocks. In addition, advantageously, the above-described upper limit suppresses a reduction in groove area ratio caused by an excessive amount of blocks, ensuring the mud performance of the tire.

Additionally, in the pneumatic tire 1, the maximum ground contact width Wb2 of the center land portion 32 with respect to the tire ground contact width TW is in the range of 0.30≤Wb2/TW≤0.60 (see FIG. 2 ). This has the advantage of appropriately setting the width Wb2 of the center land portion 32.

Additionally, in the pneumatic tire 1, the inclination angle θ1 of the first (and second) inclined lug groove 321A (321B) in the tire equatorial plane CL is in the range of 25 deg.≤θ1≤70 [deg]. This has the advantage of making the inclination angle θ1 of the inclined lug groove 321A (321B) appropriate, thus ensuring the traction characteristics of the tire.

Additionally, in the pneumatic tire 1, the distance D1 from the tire equatorial plane CL to the terminating end portion of the first (and second) inclined lug groove 321A (321B) has a relationship with the tire ground contact with TW represented by 0≤D1/TW≤0.20. Thus, the terminating end portion of the inclined lug groove 321A (321B) is appropriately positioned, advantageously improving the tire traction characteristics of the tire.

Additionally, in the pneumatic tire 1A, the inclination angle θ2 of the first (and second) lateral groove 322A (322B) with respect to the tire circumferential direction is in the range of 80 deg.≤θ2≤120 deg. (see FIG. 3 ). In such a configuration, advantageously, the lateral groove 322A (322B) is substantially orthogonal to the tire circumferential direction, advantageously improving the traction characteristics of the tire.

Additionally, in the pneumatic tire 1, the crossing angle α of the first (and second) lateral groove 322A (322B) with respect to the first (and second) inclined lug groove 321A (321B) is in the range of 30 deg.≤α≤75 deg. (see FIG. 3 ). In the configuration as described above, the lateral groove 322A (322B) connecting the inclined lug groove 321A (321B) with the circumferential main groove 2B (2A) opens laterally at an angle of 30 deg. or more relative to the inclined lug groove 321A (321B). Thus, a groove unit from the inclined lug groove 321A (321B) to the circumferential main groove 2B (2A) via the lateral groove 322A (322B) has an L-bent shape. Thus, advantageously, the terminating end portion of the inclined lug groove 321A (321B) has an increased soil column shear force, improving the traction characteristics of the tire.

Additionally, in the pneumatic tire 1, the distance D12 to the tire equatorial plane CL from the intersection point between the groove center line of each of the first and second inclined lug grooves 321A, 321B and the groove center line of the corresponding one of the first and second lateral grooves 322A, 322B has a relationship with the tire ground contact width TW represented by 0≤D12/TW≤0.20. This makes the opening positions of the first and second lateral grooves 322A, 322B with respect to the inclined lug grooves 321A, 321B appropriate, advantageously improving the traction characteristics of the tire.

Additionally, in the pneumatic tire 1, the extension length D2 of the first (and second) lateral groove 322A (322B) in the tire lateral direction has a relationship with the maximum ground contact width Wb2 of the center land portion 32 represented by 0.10≤D2/Wb2≤0.30 (see FIG. 3 ). This has the advantage of making the extension length D2 of the lateral grooves 322A (322B) appropriate.

Additionally, in the pneumatic tire 1, the maximum groove depth H3 of each of the auxiliary grooves 323A, 323B (not illustrated) has a relationship with the groove depth H1 (see FIG. 4 ) of the first (and second) inclined lug groove 321A (321B) represented by 0.70≤H3/H1≤0.90. Accordingly, the inclined lug groove 321A (321B) has an increased soil column shear force, further advantageously improving the mud performance of the tire. Additionally, the raised bottom effect of the auxiliary grooves 323A, 323B increases the rigidity of the center blocks 41A to 42B, improving the wear resistance performance of the tire.

Additionally, in the pneumatic tire 1, the edge portion of the center block 41A (41B) included in the plurality of center blocks 41A to 42B and disposed on the extension line of the first (and second) inclined lug groove 321A (321B) includes the notch portion 51 opening at the terminating end portion of the first inclined lug groove 321A (or the second inclined lug groove 321B). This has the advantage of improving the mud performance of the tire.

Additionally, in the pneumatic tire 1, the opening area Sc of the notch portion 51 with respect to the area Sb of the road contact surface of the center blocks 41A, 41B is in the range of 0.01≤Sc/Sb≤0.05. The lower limit described above has the advantage of ensuring an effect that improves soil columnar shear force by the notch portion 51. In addition, advantageously, the upper limit described above suppresses a reduction in block rigidity caused by an excessive amount of blocks, ensuring the wear resistance performance of the tire.

Additionally, in the pneumatic tire 1, the first and second circumferential main grooves 2A, 2B each have a zigzag shape with an amplitude in the tire lateral direction (see FIG. 2 ). Additionally, the pair of shoulder land portions 31A, 31B and the center land portion 32 are disposed overlapping each other in the tire circumferential direction. This has the advantage of ensuring traction characteristics on mud roads, thus ensuring the mud performance of the tire.

Example

FIGS. 8A-8C include a table showing results of performance tests of pneumatic tires according to embodiments of the technology.

In the performance tests, a plurality of different test tires were evaluated for (1) mud performance and (2) wear resistance performance. Additionally, a test tire having a tire size of LT265/70R17 121Q is assembled on a rim having a rim size of 17×8 J, and the test tire is inflated to an internal pressure of 450 kPa and loaded with a load specified by JATMA. Additionally, the test tires are mounted on all wheels of an LT pickup vehicle used as a test vehicle.

(1) In the evaluation of mud performance, the test vehicle is driven on a predetermined mud road, and a test driver performs sensory evaluation regarding traction characteristics. Results of the evaluation are expressed as index values and evaluated with the Conventional Example being assigned as the reference (100). In this evaluation, larger values are preferable.

(2) In the evaluation of wear resistance performance, after the test vehicle travels 8000 km on a predetermined offload course, the degree of wear is observed and an index evaluation is performed. Results of the evaluation are expressed as index values and evaluated with the Conventional Example being assigned as the reference (100). In this evaluation, larger values are preferable.

The test tires according to Examples have the configuration in FIGS. 1 and 2 and include the pair of circumferential main grooves 2A, 2B having a zigzag shape, the pair of shoulder land portions 31A, 31B, and the single center land portion 32. Additionally, the tire ground contact width TW is 222 mm, and the maximum ground contact width Wb2 of the center land portion 32 is 108 mm. In addition, each of the circumferential main grooves 2A, 2B has a groove width of 14.0 mm and a groove depth Hg of 14.6 mm. Additionally, each of the inclined lug grooves 321A, 321B has a groove width of 9.7 mm, and each of the lateral grooves 322A, 322B and the auxiliary grooves 323A, 323B has a groove width of 6.0 mm.

The test tires according to Conventional Example correspond to the test tires according to Example 1 in which the inclined lug grooves 321A, 321B extend through the center land portion 32 and open to the left and right circumferential main grooves 2A, 2B. Thus, the center land portion 32 does not include the lateral grooves 322A, 322B (or each of the lateral grooves 322A, 322B has the same groove depth as that of each of the inclined lug grooves 321A, 321B, thus forming a portion of each of the inclined lug grooves 321A, 321B).

As can be seen from the test results, the mud performance and wear resistance performance of the tire are improved in the test tires according to Examples. 

The invention claimed is:
 1. A pneumatic tire comprising: first and second circumferential main grooves extending in a tire circumferential direction; and a pair of shoulder land portions and one row of a center land portion defined by the first and second circumferential main grooves, the center land portion comprising: a first inclined lug groove extending at an incline with respect to the tire circumferential direction and opening, at one end portion, to the first circumferential main groove and terminating, at another end portion, within the center land portion; a second inclined lug groove extending at an incline in a direction identical to a direction of the first inclined lug groove and opening, at one end portion, to the second circumferential main groove and terminating, at another end portion, within the center land portion; a first lateral groove connecting the first inclined lug groove with the second circumferential main groove; a second lateral groove connecting the second inclined lug groove and the first circumferential main groove; first and second auxiliary grooves connecting the first inclined lug groove with the second inclined lug groove adjacent to each other; and a plurality of center blocks defined by the grooves, a groove depth H1 of the first inclined lug groove over an entire region from an opening portion to the first circumferential main groove to a terminating end portion within the center land portion having a relationship with a maximum groove depth Hg of the first circumferential main groove represented by 0.80≤H1/Hg≤1.00, and a maximum groove depth H2 of the first lateral groove having a relationship with a groove depth H1e at the terminating end portion of the first inclined lug groove represented by 0.70≤H2/H1e≤0.90.
 2. The pneumatic tire according to claim 1, wherein the plurality of center blocks include a pair of first center blocks disposed adjacent in a tire lateral direction and two or more second center blocks disposed adjacent in the tire lateral direction, the first center blocks and the second center blocks being alternately arranged in the tire circumferential direction, and the pair of first center blocks are disposed on an extension line of the first and second inclined lug grooves.
 3. The pneumatic tire according to claim 1, wherein a maximum width Lb2 of the first center blocks has a relationship with a tire ground contact width TW represented by 0.10≤Lb2/TW≤0.50.
 4. The pneumatic tire according to claim 1, wherein a distance D1 from the tire equatorial plane to the terminating end portion of the first inclined lug groove has a relationship with the tire ground contact with TW represented by 0≤D1/TW≤0.20.
 5. The pneumatic tire according to claim 1, wherein an inclination angle θ2 of the first lateral groove with respect to the tire circumferential direction is in a range of 80 deg.≤θ2≤120 deg.
 6. The pneumatic tire according to claim 1, wherein a crossing angle α of the first lateral groove with respect to the first inclined lug groove is in a range of 30 deg.≤α≤75 deg.
 7. The pneumatic tire according to claim 1, wherein a distance D12 to the tire equatorial plane from an intersection point between the groove center line of the first inclined lug groove and the first lateral groove has a relationship with the tire ground contact width TW represented by 0≤D12/TW≤0.20.
 8. The pneumatic tire according to claim 1, wherein an extension length D2 of the first lateral groove in the tire lateral direction has a relationship with the maximum ground contact width Wb2 of the center land portion represented by 0.10≤D2/Wb2≤0.30.
 9. The pneumatic tire according to claim 1, wherein a maximum groove depth H3 of the auxiliary groove has a relationship with the groove depth H1 of the first inclined lug groove represented by 0.70≤H3/H1≤0.90.
 10. The pneumatic tire according to claim 1, wherein each of the first and second circumferential main grooves has a zigzag shape with an amplitude in the tire lateral direction, and the pair of shoulder land portions and the center land portion are disposed overlapping each other as viewed in the tire circumferential direction.
 11. The pneumatic tire according to claim 1, wherein an edge portion of the center block included in the plurality of center blocks and disposed on an extension line of the first inclined lug groove includes a notch portion opening at a terminating end portion of the first inclined lug groove.
 12. The pneumatic tire according to claim 11, wherein an opening area Sc of the notch portion with respect to an area Sb of a road contact surface of the center block is in a range of 0.01≤Sc/Sb≤0.05.
 13. The pneumatic tire according to claim 1, wherein a maximum ground contact width Wb2 of the center land portion with respect to the tire ground contact width TW is in a range of 0.30≤Wb2/TW≤0.60.
 14. The pneumatic tire according to claim 13, wherein an inclination angle θ1 of the first inclined lug groove with respect to a tire equatorial plane is in a range of 25 deg.≤θ1≤70 deg. 